Now, I have gone through all the permissions and set them, using both the install guide, and the MSKB that everyone links to.
I have a newer (post hotfix) store.exe and have noticed that the "send as" permissions on my user account are being undone periodically. I did look up the fix for this, but it didn't seem very solid, just said something about restarting the service. Can anyone elaborate on that?

I did also change the reg settings to speed up the permissions cache refresh.

Any help would be much appreciated! I am hoping to move all of my treo users onto blackberrys soon

If the Send As permission keeps getting revoked then it is due to group membership. Domain Users will not lose, or shouldn't anyways, that permission but people who are part of the following groups will lose this permission:

It does count for the BESAdmin as well as the users. Yup, after removing the membership and setting the permission stop the router for 20 minutes seeing as you have applied the Mailbox cache reg key. Good catch the by way, a lot of people don't bother doing that.

Again, you ccan also follow one of the work arounds in 817433 from Microsoft as well to keep group membership.